Mufflers are installed in the exhaust system of internal combustion engines and act as acoustic soundproofing devices that reduce noise generated by the exhaust of the internal combustion engine. Mufflers may include an inlet pipe through which the exhaust gas enters the muffler, an internal expansion chamber where the exhaust gases expand to reduce noise, and an outlet pipe through which the exhaust exits the muffler for emission to atmosphere. Some muffler designs also include a double shell housing having an annular inner shell, an annular outer shell, and a layer of insulation interposed between the inner shell and the outer shell. Furthermore, in some muffler designs, the inner shell and the outer shell may be connected by inverted U-ring brackets that are welded to both the inner shell and the outer shell. The inverted U-ring brackets may each extend around a circumferential axis between the inner shell and the outer shell.
The layer of insulation between the inner and outer shells may lead to a large temperature difference between the shells as the inner shell is exposed to the high temperature exhaust gases within the expansion chamber. When exposed to the high temperature exhaust gases, the inner shell may expand (or contract) thermally, thereby subjecting the double shell housing to thermal stress that is concentrated at the welding sites between the inner and outer shells. With extended use, the thermal stress may cause cracking of the outer shell at the welding sites, leading to a shortened lifetime for the muffler. Moreover, other locations of the muffler may also be susceptible to thermal stress and weld cracking where the inner shell is constrained to another component with welded connections.
U.S. Pat. No. 4,094,644 discloses a muffler having an inner shell and an outer shell that are welded together. While effective, the welds between the inner and outer shells may be vulnerable to thermal stress when thermal gradients exist between the inner and outer shells. Thus, there is a need for improved double shell muffler designs that mitigate thermal stress at welding sites of the muffler caused by thermal expansion of the inner shell.